An Experiment in Thinking Scientifically Using Pennies and Good Sense Dennis J. Sardella Boston College, Chestnut Hill, MA 021 67 Albert Szent-Gvormil - -. once observed that discovery is seeing what everyone else has seen and thinking what no one else has thought. Anvone who has done research has had this experience, and bne can make a strong case that an introductory-level science course that does not communicate this idea (and preferably the experience of discovery itself, with its consequent exhilaration) has missed an essential point about the nature of science as a creative enterprisi Several recent articles have discussed the introduction into the instructional organic chemistry laboratory of experiments that incorporate the element of surprise ( I 3).Freshman chemistry laboratory lends itself less easily to experiences of this type because, particularly in the earlv stages of the course, students do not usually know enoigh chemistry to construct plausible and testable hvu~theses.~ Experiments done early in the semester, focusing as they often do on teaching basic laboratory mani~ulations.can often end up unintentionally making the with the resilt that studentLbegin toperopposite ceive chemistry as mechanical and unexciting. Density determinations are typical examples of such an experiment. After determining the densities of one or more known samples, students determine the density of an unknown s a m & ~ f t e n the emphasis seems to be more on obtaining the "correct" answer, and less on what can be done wi& that answer. Such experiments are unlikely to be either oarticularlv interestina - to students, or inwllectually-stimkating. We use a s i m ~ l emodification of the traditional density determination introduce students to the methodology df scientific research, as well as basic experimental technique. Students investigate the densities of a collection of pennies3and are told that the goal of this experiment is to introduce them to observation, data acquisition using basic laboratory techniques (i.e., accurate measurement of volume and mass), mathematical data analysis, graphical representation of data, interpretation of results, construction of hypotheses based on their interpretation of the data, and the design of experimental tests of their hypotheses. However, the experiment additionally incorporates " A
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h he Hungarian-born biochemist who was awarded the 1937 Nobel Prize in Medicine and Physiology for his discovery of vitamin c. 2An inquiry-based approach to freshman chemistry laboratory developed at Holy Cross College and described recently in this Journal (4) and in passing elsewhere (5),contains a brief outline of a similar ex eriment involving pennies. ?A much less elaborate experiment involving determination of the average masses of small groups of pre- and post-1983 pennies has been described by Roberts (6). 4The changed composition of pennies has been noted previously ,= ('1. 5 ~reasonable ~ o nypotheses are (a)pennles are st II made of cop per but are smaller In slze, or (0, pennles are tne same s.ze b ~are t no onger made of copper.
the element of surprise since pennies, appearances to the contrary notwithstanding, consist of two subpopulations: copper pennies (pre-1981) and copper-clad zinc pennies (posb1983)? A Three-Stage Experiment The experimental writeup given to the students prior to the laboratory period explains only the first stage of the experiment and contains explicit directions of exactly what they are expected to do, and how they are to do it. Student teams (threelteam) are given a sample of 40 assorted pennies. They determine the average density of the sample, then weigh the pennies individually, record their masses and years of minting and construct a histogram. They are then asked to propose hypotheses to explain their observations5 and suggest simple ways to test their hypotheses using only the techniques they employed in Phase I, prior to receiving directions (intentionally brief) to Phase 11. They then test their hypotheses by separating the pennies into two groups by mass and determining the average volumes of the two groups. On completing Phase 11, they frame additional hypotheses and proposc an experimental test, then are given the directions .nlno hnen for Phase 111. In Phase 111, they use the densitiea for the twoeroups - . to identil'y the metalfifrom which the pennies are made. Each team then submits a final report. Members of a team all receive the same grade for the experiment. Student reaction to the experiment has been uniformly oositive., insofar as it adds an element of detective work to what might otherwise be a rather dry procedure. On the methodoloeical level. it allows students to ex~eriencefirsthand, a n d i t an elementary level, the synbibtic interplay among observation, inference and experimental design.
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The Experiment Illustrates Two Points First, the experiment illustrates that science, like life, consists of an unending series of observations that spawn questions and can be tested by experiments, the results of which ~ r o m ustill t other auestions. This dialectic is the scientificmethod. Second, it' shows that surface appearances often can be misleading, concealing an intriguing diversity that waits to be discovered by those who are not content merelv to see (~assivelv), but who take the trouble to look (actively) beyond surf& appearances, and to think criticallv about what they observe. Only when we are actively engaged with reality does it speak to us. Copies of the experiment are available upon request. Literature Cited 1.Todd, D.; Pickeling, M. J. Chem Edue. 1988,65,11OO. 2. Picketing, M. J. Chem Educ 1890.67.436. 3. Pieketing,M. J . ChemEduc 1990,67. 524. 4. Ricci,R. W;Ditzler, M.A.J.Cham.Edlre.1931,68,229. 5. Herrick. R. S. J. Coll. Sei. X x h 1891,20,294. 6. &bees, J. L.; Hellenberg, J. L.: Postma, J. M. Ooneml Chemistry in thelobomtory; W. H. Freeman: New Yor*,1987, p 19. 7.MiUer.J. M. JChem. Educ 1881,60,142.
Volume 69 Number 11 November 1992
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